Horseradish‐Peroxidase‐Catalyzed Tyrosine Click Reaction

The efficiency of protein chemical modification on tyrosine residues with N‐methylluminol derivatives was drastically improved by using horseradish peroxidase (HRP). In the previous method, based on the use of hemin and H₂O₂, oxidative side reactions such as cysteine oxidation were problematic for functionalization of proteins selectively on tyrosine residues. Oxidative activation of N‐methylluminol derivatives with a minimum amount of H₂O₂ prevented the occurrence of oxidative side reactions under HRP‐catalyzed conditions. As probes for HRP‐catalyzed protein modification, N‐methylluminol derivatives showed much higher efficiency than tyramide without inducing oligomerization of probe molecules. Tyrosine modification also proceeded in the presence of β‐nicotinamide adenine dinucleotide (NADH, H₂O₂‐free conditions).     

Mechanism of GAPDH Redox Signaling by H2O2 Activation of a Two−Cysteine Switch

Oxidation of glyceraldehyde−3−phosphate dehydrogenase (GAPDH) by reactive oxygen species such as H₂O₂ activate pleiotropic signaling pathways is associated with pathophysiological cell fate decisions. Oxidized GAPDH binds chaperone proteins with translocation of the complex to the nucleus and mitochondria initiating autophagy and cellular apoptosis. In this study, we establish the mechanism by which H₂O₂−oxidized GAPDH subunits undergo a subunit conformational rearrangement. H₂O₂ oxidizes both the catalytic cysteine and a vicinal cysteine (four residues downstream) to their respective sulfenic acids. A ‘two−cysteine switch’ is activated, whereby the sulfenic acids irreversibly condense to an intrachain thiosulfinic ester resulting in a major metastable subunit conformational rearrangement. All four subunits of the homotetramer are uniformly and independently oxidized by H₂O₂, and the oxidized homotetramer is stabilized at low temperatures. Over time, subunits unfold forming disulfide−linked aggregates with the catalytic cysteine oxidized to a sulfinic acid, resulting from thiosulfinic ester hydrolysis via the highly reactive thiosulfonic ester intermediate. Molecular Dynamic Simulations provide additional mechanistic insights linking GAPDH subunit oxidation with generating a putative signaling conformer. The low−temperature stability of the H₂O₂−oxidized subunit conformer provides an operable framework to study mechanisms associated with gain−of−function activities of oxidized GAPDH to identify novel targets for the treatment of neurodegenerative diseases.     

Oxidation of Amino Acids,Peptides and Proteins by Ozone: A Review

The kinetics and products of the reaction of ozone with specific amino acids, peptides, and proteins are reviewed based on studies reported in the literature. Ozone reacts mainly with the unprotonated amino group of the acids and the second-order ozone rate constants for these reactions, except for cysteine, methionine, and tryptophan, vary by about two-orders from 2.6?×?10⁴ to 4.4?×?10⁶ M^?1s^?1. The site of attack on cysteine and methionine by O₃ is at the sulfhydryl rather than the amino group to give sequential O-atom addition products. The order of reactivity for the oxidation of amino acids by O₃ at pH 8 is cysteine > tryptophan ≈ methionine > phenylalanine ≈ histidine > others, with half-lives mostly in the range of milliseconds to tens of seconds (1 mg L^-1 O₃ dose). Reactions of O₃ with aliphatic amino acids form nitrate, ammonia, and one or two carbon atom-containing carbonyl and carboxylic byproducts. In the ozonolysis of peptides and proteins, oxidation by O₃ occurs at the tyrosine, tryptophan, histidine, cysteine, and methionine residues. Oxidation of proteins results in changes in their folding ability and tertiary structures.     

Iron‐Catalyzed Oxidation of Cycloalkanes and Alkylarenes with Hydrogen Peroxide

An iron‐catalyzed process for the oxidation of saturated hydrocarbons (cycloalkanes and alkylarenes) to alcohols and ketones with aqueous H₂O₂ in acetonitrile at room temperature is reported. Addition of a carboxylic acid increases the selectivity towards the ketone formation. Best results were obtained with ethylbenzene as substrate and acetic acid as additive, affording acetophenone as the main product.     

Baeyer–Villiger oxidation of cyclic ketones with aqueous hydrogen peroxide catalyzed by transition metal oxides

The Baeyer–Villiger oxidation of cyclic ketones to the corresponding lactones using aqueous hydrogen peroxide as an oxidant over transition metal oxides was investigated. MoO₃ and WO₃ were found to exhibit higher catalytic activity than TiO₂, Fe₂O₃, Co₃O₄, ZnO and ZrO₂. The high catalytic activity was attributed to the interaction of MoO₃/H₂O₂ and WO₃/H₂O₂. Additionally, the reaction mechanism on MoO₃ and WO₃ was proposed.     

An Integrated Process of H2O2 Production through Isopropanol Oxidation and Cyclohexanone Ammoximation

The possibility of the integration of the processes of H₂O₂ production through isopropanol partial oxidation and the direct ammoximation of cyclohexanone with H₂O₂ and NH₃ catalyzed by TS‐1 was investigated. The results of isopropanol partial oxidation showed that around 7.5 % yield of H₂O₂ was obtained at 110 °C, 10 atm, 2 h, and after fractionation, a H₂O₂ solution with the typical composition 25.2 wt.‐% H₂O₂, 10.3 wt.‐% isopropanol, 0.29 wt.‐% acetone, 0.45 wt.‐% phosphoric acid and 0.43 wt.‐% acetic acid was obtained. The presence of these impurities up to the above levels did not appreciably influence the ammoximation of cyclohexanone in terms of the conversion of cyclohexanone and the selectivity to cyclohexanone oxime. The results indicate that the processes of H₂O₂ production through isopropanol partial oxidation and the ammoximation of cyclohexanone can be integrated.     

A robust chemo-enzymatic lactone synthesis using acyltransferase from Mycobacterium smegmatis

The new application of acyltransferase, isolated from Mycobacterium smegmatis for the chemo-enzymatic Baeyer-Villiger oxidation of cyclic ketones to lactones was demonstrated. Acyltransferase exhibited high activity, and high stability under harsh reaction conditions, like oxidation with 60% aq. H₂O₂ at 45 °C. This paves the way to a novel robust chemo-enzymatic method for lactone synthesis with high yields.     

Improvement of the catalytic performance of lignin peroxidase in reversed micelles

BACKGROUND: Anionic surfactant sodium bis (2‐ethylhexyl) sulfosuccinate (AOT) had an inhibiting effect on lignin peroxidase (LiP). To improve the catalytic activity of LiP in an AOT reversed micelle in isooctane, nonionic surfactant polyoxyethylene lauryl ether (Brij30) was incorporated into the interfacial membrane. H₂O₂ played dual roles in the LiP‐catalyzed oxidation of substrates. To obtain a sustainable high activity of LiP, a coupled enzymatic reaction, i.e. the glucose oxidase (GOD)‐catalyzed oxidation of glucose was used as an H₂O₂ source. RESULTS: Owing to modification of the charge density of the interfacial membrane, the activity of LiP in an optimized AOT/Brij30 reversed micellar medium (χ_B (the molar percentage of Brij30) = 0.53, ω₀ ([H₂O]/([AOT] + [Brij30]) = 23, pH = 4.8) was 40 times that in a single AOT reversed micelle. Due to the controlled release of H₂O₂, the concentration of H₂O₂ in the mixed reversed micellar medium was maintained at a moderately high level throughout, which made the LiP‐catalyzed oxidation of substrates proceed at a higher conversion rate than counterparts in which H₂O₂ was supplied externally in one batch at the beginning of the reaction. Decolourization of two waterless‐soluble aromatic dyes (pyrogallol red and bromopyrogallol red) using LiP coupled with GOD in the medium also demonstrated that a higher decolourization percentage was obtained if H₂O₂ was supplied enzymatically. CONCLUSION: The proposed measures (both physicochemical and biochemical) were very effective, giving significant improvement in the catalytic performance of LiP in a single AOT reversed micelle in isooctane, which helped to degrade or transform hydrophobic aromatic compounds with LiP in reversed micelles more efficiently. Copyright © 2007 Society of Chemical Industry     

A new sol‐gel route alumina for selective oxidation of H2S to sulphur

In this study, a new synthesis method was developed for the production of modified sol‐gel alumina (SG‐M) for the selective oxidation of H₂S to elemental sulphur. The catalytic activity of this modified alumina without any active metal incorporation was then compared with the activity of commercial alumina (alumina‐com) for H₂S selective oxidation. The N₂ adsorption‐desorption isotherm showed that the SG‐M alumina synthesized in this work has a mesoporous structure with well‐defined hysteresis loops. Both alumina materials showed a γ‐Al₂O₃ crystalline phase with an amorphous structure in their crystal structure. The surface acidity of the alumina materials was determined using pyridine‐adsorbed FTIR analyses, and both alumina showed Lewis acid sites on their surfaces. The catalytic activity tests were performed at 250°C using a feed ratio of O₂/H₂S:0.5. The complete conversion of H₂S over SG‐M was achieved during 400 minutes of reaction time. However, the commercial alumina lost its activity at earlier reaction times. Lewis acid sites and surface hydroxyl groups caused the alumina to be active in H₂S selective catalytic oxidation, and the formation of Al‐S bonds, observed when the H₂S conversion fell, caused a decrease in the catalytic activity of the alumina materials. A high sulphur yield (≥95%) was obtained over SG‐M, even though there was no active metal incorporation and even in the presence of excess oxygen. Considering the catalytic activities, the new sol‐gel alumina synthesized in this work is superior to commercial alumina. It was concluded that, as a catalyst without any active metal, SG‐M is a promising catalyst in H₂S selective oxidation to sulphur.     

Selective Oxidations on Recoverable Catalysts Assembled in Emulsions

Catalysts assembled in emulsions are found to be potentially recoverable and efficient for a number of catalytic reactions. The catalysts composed of polyoxometalate anions and quaternary ammonium cations have been designed and synthesized according to the catalytic reactions and by optimizing the structures of cations and anions. The catalysts act essentially as surfactants, which are uniformly distributed in the interface of the emulsion droplets, and accordingly behave like homogeneous catalysts. The catalysts show remarkable selectivity and activity in the oxidation of sulfur-containing molecules to sulfones in diesel and the selective oxidation of alcohols to ketones, using H₂O₂ as oxidant. For an example, the catalyst demonstrated over 96% efficiency of H₂O₂ and ˜100% selectivity to sulfones for the selective oxidation of sulfur-containing molecules in real diesel. Moreover, the catalysts can be separated and recycled by a simple demulsification and re-emulsification.     

Clean Baeyer–Villiger Oxidation Using Hydrogen Peroxide as Oxidant Catalyzed by Aluminium Trichloride in Ethanol

Baeyer–Villiger oxidation of ketones was carried out using AlCl₃ as catalyst, H₂O₂ (30%) as oxidant in innocuity and environmentally friendly ethanol conditions. Cyclic ketones and acyclic ketones were transformed into the corresponding lactones or esters in 5–24 h at 40–70 °C with very high conversion and selectivity. A possible reaction mechanism was also given.     

Catalytic partial oxidation of CH4 over bimetallic Ni‐Re/Al2O3: Kinetic determination for application in microreactor

The activity of a novel Ni‐Re/Al₂O₃ catalyst toward partial oxidation of methane was investigated in comparison with that of a precious‐metal Rh/Al₂O₃ catalyst. Reactions involving CH₄/O₂/Ar, CH₄/H₂O/Ar, CH₄/CO₂/Ar, CO/O₂/Ar, and H₂/O₂/Ar were performed to determine the kinetic expressions based on indirect partial oxidation scheme. A mathematical model comprising of Ergun equation as well as mass and energy balances with lumped indirect partial oxidation network was applied to obtain the kinetic parameters and then used to predict the reactant and product concentrations as well as temperature profiles within a fixed‐bed microreactor. H₂ and CO production as well as H₂/CO₂ and CO/CO₂ ratios from the reaction over Ni‐Re/Al₂O₃ catalyst were higher than those over Rh/Al₂O₃ catalyst. Simulation revealed that much smoother temperature profiles along the microreactor length were obtained when using Ni‐Re/Al₂O₃ catalyst. Steep hot‐spot temperature gradients, particularly at the entrance of the reactor, were, conversely, noted when using Rh/Al₂O₃ catalyst. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1691–1701, 2018     

Characterization and catalytic activity of polymer supported ruthenium Schiff base complexes towards catechol oxidation

Ruthenium(III) complexes of the Schiff bases formed by the condensation of polymer bound aldehyde and the amines, such as 1,2‐phenylenediamine (PS‐opd), 2‐aminophenol (PS‐ap), and 2‐aminobenzimidazole (PS‐ab) have been prepared. The magnetic moment, EPR and electronic spectra suggest an octahedral structure for the complexes. The complexes of PS‐opd, PS‐ap, and PS‐ab have been assigned the formula [PS‐opdRuCl₃(H₂O)], [PS‐apRuCl₂(H₂O)₂], [PS‐abRuCl₃(H₂O)₂], respectively. These complexes catalyze oxidation of catechol using H₂O₂ selectively to o‐benzoquinone. The catalytic activity of the complexes is in the order [PS‐abRuCl₃(H₂O)₂] ? [PS‐opdRuCl₃(H₂O)] ? [PS‐apRuCl₂(H₂O)₂]. Mechanism of the catalytic oxidation of catechol by ruthenium(III) complex is suggested to take place through the formation of a ruthenium(II) complex and its subsequent oxidation by H₂O₂ to the ruthenium(III) complex. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Process integration of H2O2 generation and the ammoximation of cyclohexanone

The possibility of the integration of the processes of H₂O₂ generation through isopropanol partial oxidation and ammoximation of cyclohexanone with H₂O₂ and NH₃ TS‐1 catalysed was investigated. The ammoximation of cyclohexanone over TS‐1 with isopropanol as solvent was first studied. The results show that isopropanol can be used as solvent, and the impurities in the H₂O₂ solution obtained through isopropanol oxidation with only acetone needing to be separated have no harmful effects on the ammoximation of cyclohexanone, suggesting that the process of H₂O₂ generation through isopropanol oxidation and the ammoximation of cyclohexanone could be directly integrated. Copyright © 2004 Society of Chemical Industry     

Heterogeneously assisted oxidation of adsorbates from carbonmonoxide, methanol and ethanol by hydrogen peroxide solutions on platinum electrodes in sulphuric acid

The influence of hydrogen peroxide on the adsorption and oxidation of carbon monoxide, methanol and ethanol adlayers on porous Pt electrodes were studied in 2 M sulphuric acid solution by means of cyclic voltammetry and differential electrochemical mass spectrometry (DEMS). The oxidation of adsorbed species is observed at electrode potentials far less negative than those required for electrochemical adsorbate oxidation. The oxidation by H₂O₂ is dependent on its concentration in solution, as well as on the adsorbates and their coverages. In all cases the isolated adlayers are oxidised by dissolved H₂O₂. However, the presence of H₂O₂ during adsorption partially inhibits adlayer formation from CH₃OH and C₂H₅OH, but avoids almost completely the adsorption of carbon monoxide. The removal of the residues from the surface by dissolved hydrogen peroxide probably occurs through O_ad species formed during the heterogeneous decomposition reaction of H₂O₂ on Pt.     

Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide

Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H₂ to H₂O₂ (at 295 K) in acidic medium (0.02 M H₂SO₄) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H₂O₂, N₂O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H₂-to-H₂O₂ conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO₂ < Pd/ThO₂ < Pd/Ga₂O₃. The H₂ oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H₂O₂ decomposition activity of the catalysts. There exists a close relationship between the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity in the oxidation process and the H₂O₂ decomposition activity of the catalysts; the higher the H₂O₂ decomposition activity, the lower the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity.     

Kinetic study of the manganese‐based catalytic hydrogen peroxide oxidation of a persistent azo‐dye

BACKGROUND: The discharge of synthetic dyes by the textile industry into the environment poses concerns due to their persistence and toxicity. New efficient treatment processes are required to effectively degrade these dyes. The aim of this work was to study the degradation of a persistent dye (Drimarene Brilliant Reactive Red K‐4BL, C.I.147) using H₂O₂ oxidation catalysed by an Mn(III)‐saltren catalyst and to develop a kinetic model for this system. RESULTS: Dye oxidation with H₂O₂ was significantly improved by the addition of the catalyst. As the pH was increased from 3 to 10, the oxidation rates increased significantly. The kinetic model developed in this study was found to adequately explain the experimental results. In particular, dye oxidation can be described at high pH by pseudo‐first‐order kinetics. A Michaelis–Menton type equation was developed from the model and was found to adequately describe the effect of H₂O₂ and catalyst concentrations on the apparent pseudo‐first‐order rate constant. Optimum catalyst and H₂O₂ concentrations of 500 mg L^?1 and 6.3 g L^?1, respectively, were found to give maximum reaction rates. CONCLUSION: Catalytic H₂O₂ oxidation was found to be effective for the removal of persistent dye and the results obtained in this work are of significance for design and scale‐up of a treatment process. Copyright © 2009 Society of Chemical Industry     

Unusual Activity Enhancement of NO Conversion over Ag/Al2O3 by Using a Mixed NH3/H2 Reductant Under Lean Conditions

Addition of H₂ to a NO/NH₃/O₂/H₂O feed for selective catalytic reduction of nitrogen oxide over Ag/Al₂O₃ catalysts causes an unusual enhancement of activity, e.g., the marginal activity (<10%) of 1 wt% Ag impregnated on γ-Al₂O₃ or mesoporous Al₂O₃ modifications is boosted to nearly 100% over a broad temperature range from 200 to 550°C at a space velocity of 30,000cm³g^?1h^?1). Contrary, silver on SiO₂ or α-Al₂O₃ shows no improvement of activity in the presence of H₂. The effect is tentatively attributed to a higher percentage of intermediary nano-sized Ag clusters on high-surface area Al₂O₃ in the presence of hydrogen. This promotes oxygen activation and hence NO oxidation to reactive intermediate nitrite species. The required dispersion of Ag cannot be stabilized on SiO₂ or α-Al₂O₃.     

Affinity‐tuned peroxidase‐like activity of hydrogel‐supported Fe3O4 nanozyme through alteration of crosslinking concentration

In this work, we evaluated the effect of crosslinking concentration on the affinity of poly (2‐acrylamido‐2‐methyl‐1‐propansulfonic acid) (PAMPS) hydrogel‐supported Fe₃O₄ nanozyme towards substrates (tetramethylbenzidine (TMB) and H₂O₂). The peroxidase‐like catalytic activity of PAMPS/Fe₃O₄ nanozyme was discussed with respect to crosslinking concentration of PAMPS hydrogel for the oxidation of TMB in the presence of H₂O₂ at room temperature. High catalytic activity was achieved due to good dispersion of Fe₃O₄ nanozyme in the hydrogel network and strong affinity of PAMPS hydrogel‐supported Fe₃O₄ nanozyme towards substrates. The affinity between the hydrogel‐supported Fe₃O₄ nanozyme and substrates can be improved by regulating the crosslinking concentration of PAMPS hydrogel without other trenchant experimental conditions. In addition, the result indicated that H₂O₂ can be detected even at a concentration as low as 1.5 × 10^?6 mol L^?1 with a linear detection range of 1.5–9.8 × 10^?6 mol L^?1. Such investigations not only showed a new approach to improve the affinity and peroxidase‐like activity of Fe₃O₄ nanozyme, but also verified its potential application in bio‐detection and environmental chemistry. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43065.     

An optimization and modeling approach for H2O2/UV‐C oxidation of a commercial non‐ionic textile surfactant using central composite design

BACKGROUND: Industrial surfactants are biologically complex organics that are difficult to degrade and may cause ecotoxicological risks in the environment. Until now, many scientific reports have been devoted to the effective treatment of surfactants employing advanced oxidation processes, but there is no available experimental study dealing with the optimization and statistical design of surfactant oxidation with the well‐established H₂O₂/UV‐C process. RESULTS: Considering the major factors influencing H₂O₂/UV‐C performance as well as their interactions, the reaction conditions required for the complete oxidation of a commercial non‐ionic textile surfactant, an alkyl ethoxylate, were modeled and optimized using central composite design‐response surface methodology (CCD‐RSM). Experimental results revealed that for an aqueous non‐ionic surfactant solution at an initial chemical oxygen demand (COD) of 450 mg L^?1, the most appropriate H₂O₂/UV‐C treatment conditions to achieve full mineralization at an initial pH of 10.5 were 47 mmol L^?1 H₂O₂ and a reaction time of 86 min (corresponding to a UV dose of 30 kWh m^?3). CONCLUSION: CCD allowed the development of empirical polynomial equations (quadratic models) that successfully predicted COD and TOC removal efficiencies under all experimental conditions employed in the present work. The process variable treatment time, followed by the initial COD content of the aqueous surfactant solution were found to be the main parameters affecting treatment performance, whereas the initial H₂O₂ concentration had the least influence on advanced oxidation efficiencies. The H₂O₂ concentration and surfactant COD were found to be more important for TOC abatement compared with COD abatement. Copyright © 2009 Society of Chemical Industry